Magnetic Field Confinement of Laser Irradiated Solid Particle Plasmas

Abstract

Laser irradiation of a small solid particle of lithium hydride in vacuum results in the generation of a spherically symmetric, isolated, highly ionized plasma. Experimental studies with such plasmas formed within mirror and minimum-B magnetic field up to 8 kG show that the expanding plasma can be captured by the magnetic field and the expansion kinetic energy thermalized, in agreement with a simple magnetohydrodynamic model of the plasma-magnetic field interaction. In the experiments, the major plasma loss occurs through the mirror loss cones, and mass spectrometer measurements show rapid escape of the highly ionized lithium followed by a more gradual decay of hydrogen indicating a scattering mechanism for the plasma decay. Plasmas with densities of 3 × 1013 cm−3 at temperatures of 100 eV are confined for lifetimes up to 150 μsec in a minimum-B field compared with the 0.3 μsec lifetime associated with the free plasma expansion. Both the magnitude and the temperature dependence of the plasma decay from a minimum-B containment field are consistent with plasma loss by Coulomb collisional scattering into the magnetic field loss cones.

Collisionless coupling of a high-β expansion to an ambient, magnetized plasma. I. Rayleigh model and scaling

“…1 along with experimental data that the author was able to extract from several high-b expansion experiments that had sufficiently clear and complete RðtÞ curves. [22][23][24] : Figure 2 shows a selection of the excellent agreement between these quantities over wide variation in B 0 . Note that the 4 points following the blue line, s D $ B À2 0 , were points for which the assumption b ) 1 was likely broken and the authors of that paper also pointed to a degraded quality of confinement of their MLPP.…”

Production and initial characterization of a laser-induced plasma in a pulsed magnetic field for atomic spectrometry

“…Instead, an estimate of the dB/dt during the first quarter-cycle was calculated based on the peak value of Bz. For a simple RCL circuit, the time to reach the first current maximum (t) may be estimated by (4) .00, (E) 2.00, (F) 5.00, (G) 10.00 /uH; wire diameter, 1.7 mm; coil radius, 15 mm. An estimate of dB/dt, then, may be calculated by dividing Bz by t. Figure 4b shows how dB/dt varies with n for the same values of Laya investigated in Figure 4a. Laya has a profound effect on dB/dt, so much so that single-turn coils are most efficient for systems having a residual circuit inductance less than about 100 nH.…”

“…Physicists have successfully investigated electromagnetic compression techniques for confinement and heating of laser-induced plasmas (10)(11)(12)(13)(14)(15). This approach seems especially attractive for spectrochemical analysis as it requires no direct electrode contact with the plasma; in addition, compression/ confinement of the plasma results in an increase in the plasma power-density which should enhance atomization efficiencies.…”

“…Effect of number of turns on (a) peak magnetic field and (b) dB/dt. Model system parameters are as follows: V0 = 9.5 kV; C = 24 nF\ Laya = (A) 0.010, (B) 0.100, (C) 0.500, (D) 1.00, (E) 2.00, (F) 5.00, (G)10.00 /uH; wire diameter, 1.7 mm; coil radius,15 mm.…”

Laser-fusion program. Semiannual report, January--June 1973

“…Features o Basic feasibility demonstrated -;> 70% of keV fireball imarnal energy converted to compressed m jc field energy (Haught et al, 1970) o Low magnetic field intensities suitable -2-4 Tesla for 10' joule microexplosions o 500-5000 kV, -1 Msec time pulses available for direct transmission line excitation, or for transformation DC field-generating current system…”